Historical clue formulations

• Didn't exist — 2016-04-17
• "You ___ kidding!" — 2010-02-21
• "You ___ kidding!" — 2008-04-18
• Failed to be — 2006-12-01
• "You ___ kidding!" — 2005-12-09
• Cole Porter's "___ We Fools?" — 2002-04-27
• "You ___ kidding!" — 1996-10-03